1. Field of the invention
The present invention relates to a camera body and, more particularly, to a camera body that performs picture taking using a photographic photosensitive film.
2. Related background art
A diversity of constructions have been proposed for the main body of a picture-taking camera (hereinafter simply referred to as a camera) that performs picture taking using a roll of photographic photosensitive film (hereinafter simply referred to as film) or other photosensitive materials.
Cameras as disclosed in Japanese Unexamined Patent Publications No. 8-160516 and Japanese Unexamined Patent Publication No. 2-259631, incorporate a unitized design in which a plurality of units, each constructed for its own function, are integrated into a unitary body in an efficient manner to form the camera body while assuring the robustness of the camera body.
Even when an external force acts on the camera body, the above design controls deformation of a guide rail and other components forming a film path within the camera and maintains the flatness of the film therein. When any change in specification is necessary, corresponding design change is carried out on a unit by unit basis. The time required for the design change is thus shortened, and a modification in the manufacturing facility is kept to a limited range.
A unit (hereinafter referred to as an aperture unit) defining a picture-taking opening (also referred to as an aperture) is provided with guide rails that project rearward by a predetermined length in a direction parallel to an optical axis and that runs in the vicinity of the upper inner edge and the lower inner edge of the unit. The guide rails and a pressure plate arranged on the rear side in the camera typically defines the position of the film loaded in the camera body in terms of the width direction of the film and the direction of the optical axis.
Such an aperture unit of this conventional camera is typically provided with a pair of first guide rails that define the position of the film in its width direction and a pair of second guide rails that are arranged within the first guide rails to define the film position in the optical axis direction, thereby assuring the flatness of the film.
A small gap or tunnel gap between the second guide rails and the pressure plate forms a film path. Since the surfaces of the guide rails forming the film path require an extremely high machining accuracy, a high-precision plastic molding process, milling operation or other technique is used to achieve the required accuracy level.
When the aperture unit is manufactured from a metal material such as aluminum or aluminum alloy, a milling cutting process is typically used to precisely machine the rail surface of the guide rails in the unit. The milling cutting process requires high manufacturing skill, thereby unavoidably pushing up the cost of production.
When the means such as the milling cutting process is used on the metal aperture unit, a bending process is also needed to assure accuracy. This means not only degrades the production efficiency but also increases the cost of production.
When the aperture unit is constructed of a plastic material as is recently in widespread use, the rail surface of the guide rails is easily formed, but the plastic member fails to meet the strength that is required of the aperture unit. There is thus a possibility that the aperture unit itself may become deformed during use or transportation, and a deformed unit may present a problem with maintaining the flatness of the film.